Telephone-repeater circuits



Dec. 22 1925. 1,566,311

f A. B. CLARK ET AL TELEPHONE REPEATER CIRCUIT S l/ 4 Il ATTOQNEY Dec. 22l 1925.

A. B, CLARK *AL TELEPHONE REPEATER CIRCUITSl .Filed oct. 1921 2 Sheets-Sheet 2 ,6 l ooooooooooob 19;" m G0 un. w

fly. 7 v NVENTORS w/M/m/@ff ATTORNEY .Patented Bee. 212, 1h25.

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' .entre a. citaten, or annemarie, Nn'w'Yoari, ann naar s. Horn', or RIDGEWOOD, NEW

sanear, assienoiis ro einsamen raitnrisonn .ann rannanarn COMPANY, A

UDRGB'ATN 0F NEW YGRBI.

TELEPHONE-REPEATER CIRCUITS.

Application filed ctober 3, 1921. Serial No. 504,976.

To azz whom a may mm:

Be it known that we, ALVA B. CLARK and RAY S. Horr, residing at Brooklyn and Ridgewood, in the counties of Kings and' Bergen and States of New York and New Jersey, respectively, `have invented certain Improvements in Telephone-Repeater Gir lines in such a manner that there will be equal iiniedances on each side of the repeater. till another object of our invention relatesto the interposition of suitable networks between a 21-type repeater and one or both of two dissimilar lines onnected thereto, so that the impedances of the lines may be equalized and transmission through the repeater may4 be ei'i'ected without im pedance unbalance. of our invention willv become apparent on consideration of a limited number oi' specific embodiments of the invention which we have indicated in the accompanying'drawings and will now proceed to discuss, with the underthe appended claims.

Referring to the drawings, Figure l is a diagram illustrating` equalization of imlpedances tor the case of two lines having a.

constant and real impedance ratio, Figs. Q.

and 2" are diagrams illustrating alternative systems for the same case, Fig. 3 is a diagram illustrating the equalization of two similar loaded lines having .different lengths of endsections at the repeater, Fig. 4 is a diagram illustrating equalization of impedances for a loaded-line and a non-loaded line, Fig. 5 is a diagram illustrating the case of two loaded lines of diderent irnpedances,v

Fig. 6 is a diagram illustrating a modification of detail in Figs. 4 or 5 and Fig. 7 is a diagram for two smooth open-wire lines of diieren't characteristic impedances.

It will be understood that the so-called 21-type repeater is of the character shown in Fig( 1. The input terminals of the re'- These and other objectspeating element 15 are bridged across the line, being connected to the middle points of the series windings 13. The amplified current delivered by the repeater element 15 goes to the winding 14 which stands in inductive relation with the' series windings 13; the current induced therein i-s sent equally in each direction along the line. In order that none of the amplified energy delivered from the repeater element 15 through the coil 14 to the coils 13 shall get back to the input side of the repeater 15, it is highly important that the lines shall be balanced, that is, that they shall' offer the same impedance looking each way from the lniiddle points of the coils-13. If this condition is not realized, some of the amplified energy from the repeater element 15 will get back to the input circuit and singing will resuit.

lAccordingly, unless some ,provision 'is ferent characteristic impedance. standing that the invention will be defined 1n f The invention will be explained by con sidering certain simple cases at the outset and then utilizing the principles developed, in connection with more general and'complex cases. Fig. 1 assumes the case of two lines having different characteristic impedances but subject to the condition that the ratio of these impedances is constant and real for all frequencies within the useful range. An example would be afforded b'y .a pair ofA loaded Alines having a: different -weight of loading but having the same fractional end sections adjacent to the repeater and having equal critical frequencies. V

Under the condition here supposed, an autdtransfornnr-- )16, is interposed between the low impedanceline 11 and the repeater. This has the proper ratio so that it equalizes the impedances looking each way from the repeater along the two lines 11 and 12.

In practical cases the auto-transformer 16 will not merely change the apparent impedmodali scribed for the earlier figures. The capacity of a condenser to balance the reactanceof a non-loaded line is given by the formula am R where L, C and A1t are respectively the distributed inductance, capacity and resistance "of the line per unit length. The capacity so found is divided by the impedance ratio of the An.uto-transiormer 16, to find the joint capacity of the twol condensers 32 in series.

Between the amplifying elementv and the output winding 14 we put a low pass 15 filter 33 with its critical frequency at 85% of the critical frequency of the loaded line 2G. As we have just stated, the 0.8 section ending of the loaded line that was secured by the condenser 29 equalized the resistance 2 component only for about 85% of the range up to the critlcal frequency of the loaded line., The filter 33 is designed to cut off all frequencies above the frequency at which the resistance lcomponent becomes inconstant.

Fig. 5 presents the case for two loaded lines of different characteristic impedances. It will be seen that in the same manner stated for Fig. 4, we build each loaded line .3 out to a 0.8 section termination to make its resistance component as nearly uniform as f/fpossible, then introduce a reactance annulling network on each side, thus reducing the case to that of Fig. 1.

35 yAn alternative arrangement by which the impedance of the line can be made to ap-' of the inductance of the normal coil 28 and a combination consisting of a condenser 34 and inductance 35 in series is bridged across the terminals. From this point the equalization'of the impedance will be the. same as in Figs. 4 or The impedance of different non-loaded lines may differ in magnitude. Their reactanccs will differ from cach other in such a way that the difference can be compensated by means of'series condensers 32 as illustrated in Fig. 7, which assumes an S-gauge open-wire line 36 on the left and a l2-gauge open-wire line 37 on the right. The con- Adensei's 32 of suitable capacity interposed in thc line 36 serve to compensate for the difference in rcactance. iis leaves the case of tu'o lines with@ their impedance ratio a real constant for which the construction over the essential frequency range, means to 1 shown if lill Y, 1 suffices to complete the dia- 00 gram. lie-.capacity of the condensers 32 isV computed as follows. Compute the capacity C, necessary vto balance the reactance of the line 36, and the capacity to balance the reactance of the line 37. Multiply the latter by the impedance ratio of the autotransformer l16 and call the result C2. Then the joint capacity of the condensers 32 in series is .CF-Vwo.

equalize the'resultant impedancesof the two lines, and a wave filter associated with said repeater and having a critical frequency corresponding" to said essential frequency range. 3. In combination, two dissimilar lines, 'a 21type repeater connecting them, and an interposed transformer on one side to equalw ize the impedances of the ltwo lines.

4. In combination, two dissimilar lines, a 21-type repeater connecting them, an interposed transformer on one side to equalize the impedances of the two lines, and a retardation coil or transformer on the 4other side to match said interposed transformer.

5. In combination, two dissimilar lines, at least one of them being a loaded ling, and means to equalize their impedances comprising elements to build out the. loaded line tothe proper fractional sectional ending.

6. In combination, two dissimilar lines, at

leasty one of them being a loaded line, elements building the loaded line out to 0.8 of a normalelement thereof. a reactance annulling network associated therewith, a repeater, a transformer between one line and the repeater, a retardation c'oil or transformeracross the other ,line, and a low pass Wave filter associated with the repeater.4

I n testimony whereof, we have signed our names to this specification this 27th day of 115 September, 1921. y

ALVA B. CLARK. RAY Si. HOYT. 

